Yes, all plants put lots of protein in their seeds to give their offspring plenty of resources to get off to a good start. This does not mean that there are not major differences in protein content between the seeds of different types of plants. OP asked about legumes vs non legumes, not seeds vs other parts of plants.

Comparing protein content on a per cup of the food as it is eaten is going to give you a misleading answer to the question. We add water to black beans while cooking before we eat them, which increases the volume of the beans, so fewer beans and less of the protein they contain, fit in a cup after cooking than before. Eating a half cup of pistachios will leave you much more full than eating a cup of black beans. It is more meaningful to compare foods on a dry weight basis, so how much protein per 100g of dry peas, wheat, rice or nuts.

Peas and beans have 20-25g of protein (there are lots of different species, so some may be higher or lower), wheat is 8-15g (some may get higher, different types of wheat have different protein contents), rice is 10-12g. Tree nuts are in the 20g range, so close to legumes, but remember they are trees with huge root systems. It is not surprising their seeds are different from non legume annuals like rice and wheat.